Please refer to FIGS. 1, 2A and 2B, a conventional crib frame 10 includes a frame 20, a bottom frame 30 and four connection planks 40. The frame 20 has four corner pillars 21 at four corners each having a row of cavities 211 formed thereon. Each connection plank 40 has a first aperture 41 at one end corresponding to one orifice 32 on the vertical surface of a width side 31 of the bottom frame 30 and run through and fastened by a first screw 42. The connection plank 40 has a second aperture 43 at another end run through by a second screw 44 and fastened to one of the cavities 211. When a baby grows gradually to prevent the baby from crawling outside the crib the connection planks 40 can be adjusted by changing the fastened cavities 211 to lower the height of the bottom frame 30.
As shown in FIG. 2A, the aforesaid structure has a drawback, i.e. in the event that the bottom frame 30a is a smaller size with a narrower width on the two width sides 31a the two orifices 32 are shrunk inwards compared with that of the width sides 31 of the larger bottom frame 30. Hence when the connection planks 40 are fastened to the lowest cavities 211 and the bottom frame 30a is fastened to the first aperture 41, the bottom frame 30a is raised, added the height of the mattress (not shown in the drawings), the baby in the crib can easily crawl outside the frame 20 and risk in injury. Moreover, with the connection planks 40 fastened axially on the vertical surface of the two width sides 31, as shown in FIG. 2B, the first screw 42 is subject to a great shearing force; in addition, with the width sides 31 narrower than the frame 20, a gap is formed between them, and swaying of the bottom frame 30 takes place when the baby is moving in the crib (as shown by the arrows in FIG. 2A), the screws 42 and 44 are easily loosened and worn, and could result in broken and collapse of the bottom frame 30 after a period of time and cause injury of the baby.